free_listener_handle

In the data receiving example in C/C++, what is the free_listener_handle() being referenced several times? Visual studio linker gives LNK2019 error saying this object cannot be found. I checked the neurosdkxxx dll files and the closest I can see in that is free_param_listener_handle(). The latter seems to allow linking, but the exe then executes erratically.

Is the free_listener_handle defined in some other file?